1. Field of the Invention
The invention relates to a belt tensioner of the type for automotive vehicles.
2. Description of the Related Art
Typical belt tensioners are known, for example from DE-A-43 27 141 or DE-A-40 10 928. These belt tensioners are employed in motor vehicles for tightening the V-belt and comprise a retainer with a tension arm, which is fitted with an idler pulley at one end, that is applied to the belt, and which is joined to a radial plain bearing at its other end. The radial plain bearing includes a bearing bush part and a bearing pin part, whereby one of the parts is fixed to the tension arm and the other part is held spatially fixed. A rotary spring in the form of a spiral coil spring is wrapped coaxially around the bearing bush and bearing pin and is held by one end on the retainer and held spatially fixed at the other end. These known belt tensioners are fitted in a state in which the bearing bush and the bearing pin have been rotated against one another under the pretension of the rotary spring, so that the idler pulley already exerts a predetermined force on the belt. Due to the spring force of the pretensioned rotary spring, the belt is held under a predetermined tension, but the idler pulley can deflect or take up the slack if the length of the belt changes.
Due to the type of construction, the tension arm bearing the belt idler pulley must, however, be arranged off center in relation to the axial length of the radial plain bearing on the bearing bush or bearing pin. Consequently, the radial plain bearing is, however, stressed by tilting forces which cause increased wear. Attempts have been made in DE-A-43 27 141 to arrange the deflecting point of the swivel spring in the axial direction to the rotating axis so far removed from the radial plain bearing that the resultant of the force introduced into the radial plain bearing meets approximately the center of the axial length of the radial plain bearing. This is however only possible where there is sufficient installation space available.
The object of the invention is to develop a belt tensioner such that the susceptibility to wear is reduced with a compact, short construction.